He worked for Municipal Architect Albert L. Harris and for Arthur B. Heaton and Philip M. Jullien before opening his own office in 1932.
Over the next twenty years Chatelain developed a large and diverse practice centered on Washington.
[1][2] Chatelain joined the American Institute of Architects (AIA) in 1930 as a member of the Washington chapter.
[2] After his death, in recognition of his work Easterseals created the Leon Chatelain Award for "outstanding leadership in advancing barrier-free environments for people with handicaps.
[2] Two buildings designed by Chatelain and his associates have been listed on the United States National Register of Historic Places.